There are many applications where it is necessary to repeatedly dispense a metered or measured quantity of liquid from a bottle, generally, the bottle in which the liquid is received from a supplier. Further, bottle top dispensers of different designs have been known for many years for servicing those applications. Typically, such dispensers utilize a plunger and cylinder mounted on top of the bottle. Often such dispensers have two check valves, a fill check valve and a dispense check valve. When the plunger is withdrawn, the fill check valve permits liquid to flow from the container into the cylinder, and the dispense check valve prevents the liquid from flowing out of the dispenser. However, we the plunger is advanced, the dispense check valve permits the liquid to flow from the cylinder to a dispensing orifice; and the fill check valve prevents the liquid from re-entering the container. The plunger often has an adjustable stop such that withdrawal of the plunger to the stop position pulls a desired volume of liquid from the bottle into the cylinder; and a subsequent advancement of the plunger in the cylinder pushes the desired volume of liquid out through the dispensing orifice.
In many applications the liquid being dispensed may be a chemical reagent, or corrosive, or toxic and/or a very expensive liquid. In those applications, it is desirable to minimize unnecessary dispensing of the liquid, for example, as often occurs when initially purging air from the dispenser. To prevent accidental or unnecessary dispensing of the liquid, U.S. Pat. No. 4,306,670 discloses a flexible tube attached to the dispensing tip, the end of which may be inserted in a hole in the dispenser housing, thereby recirculating the liquid. However, the flexible tube itself presents a potential for an accidental leakage of liquid therefrom and therefore, must be handled with extreme care and caution.
Another bottle top dispenser with a recirculation capability is disclosed in the European Patent Publication No. 542 241 A2. In that publication, the fill and dispense check valves are mounted in the dispenser body; and a recirculation valve is mounted in the dispensing spout or tip. Generally, the recirculation valve is rotatable between two positions, a first position permits liquid to be dispensed from the tip and, a second position causes the liquid to be recirculated through the spout, through the dispenser body and back into the bottle. In each of the several embodiments disclosed, the recirculation valve is designed to have separate dispense and recirculate paths there through depending on the valve position. The above design has several disadvantages. First, mounting the recirculation valve in the dispensing tip requires that dispenser tip be large and bulky. Such a design not only adds costs but may not be as pleasing in appearance as the more traditional sleeker, thinner dispenser tip designs. Second, by requiring separate dispense and recirculate paths through the recirculation valve substantially increases the complexity and cost of the recirculation valve.
Therefore, there continues to be a need to provide a bottle top dispenser providing selectable dispensing and recirculation capabilities that is compact, simple in design, easy to use, and less expensive to manufacture.